Surgical procedures to replace a complete or partial knee joint with a prosthetic implant are becoming increasingly common, with high rates of success. Total joint replacement is usually performed to relieve pain and restore function caused by damaged or malfunctioning joints.
In addition to replacing the diseased natural knee with femoral and tibial prostheses, the knee joint replacement procedure typically involves resurfacing the articular surface of the patella because in some cases the natural bone of the patella does not interface well with the materials used in constructing the prosthesis, and this can result in great pain to the patient. In most cases, the patella is resurfaced with a prosthetic component, or patellar button which may be made from ultra high molecular weight polyethylene.
Implantation of resurfacing components to the patella, in combination with the prosthetic knee joint if improperly aligned, can result in an undesirable alteration of the load distribution imparted to the prosthesis and supporting bone structures. Normal daily activity, such as walking, causes flexion and extension of the quadriceps mechanism, patellar ligament, and associated tendons. These movements in turn exert loads on the attached and surrounding anatomical or prosthetic structures.
In total knee joint replacement, it is critical to achieve uniform and properly oriented load transfer from the implant to the supporting bone. To accomplish this, it is desirable to recreate the loading patterns which are imparted to the supporting bone prior to placing the implants, as occurs in a normal, naturally functioning knee. These loading patterns are primarily compressive and adverse bone remodelling can result if atypical loading patterns, including shear, are introduced in the total knee procedure. It is thus desirable to accurately orient the implants to recreate normal stress patterns in supportive bony structure. When the patella is properly resected, the resultant force active on the patella will be generally perpendicular to the main plane of the patella, resulting in primarily compressive forces being imparted to the supporting bone. In this manner, the desired loading patterns may be recreated, imparting primarily compressive loads on the supporting bone to imitate the normal, natural condition.
Several devices are known in the prior art for resecting the articular surface of the patella. These commonly involve pliers or scissors-like mechanisms which grasp the patella. The surgeon is required to orient the patella in the device by visual approximation, relying on judgment for proper positioning and orientation. Available resection guides do not provide a reference to bony or soft tissue structures. The patella is then resected by placing a saw through the resection guide and sawing the patella. In the event of inaccurate or improper orientation of the patella within the device, the depth or angle of resection will be incorrect. This will result in an improper distribution of forces to the new knee joint, and adverse loading of the supporting bone structures may result.
What is clearly needed, therefore, is a device and method which will aid the surgeon in establishing an accurate and repeatable orientation of the patella during a resection procedure so as to enable proper orientation of a subsequently implanted patellar implant.